1. FIELD OF THE INVENTION
This invention relates to a water resistance load system used for measurement or testing of output characteristics of generators and various other electric power source devices including inverters.
2. DESCRIPTION OF THE PRIOR ART
The water resistor has heretofore been used as a load system of the type noted. FIG. 1 shows a water resistor .alpha.. It comprises three electrode plates (or electrode cylinders) b, to which three-phase high pressure cables a are connected. The electrode plates b are suspended from a support d provided on a water trough c about 3 m in each side and 2 m in height. The extent of immersion of the electrode plates in the water is controlled to control the load, and the output power of the power source device is consumed with water in the water trough c as a resistor. As power is consumed, the water temperature is gradually increased to increase the electric conductivity of the water. This means that dielectric breakdown of the water will eventually occur to generate a dangerous electric arc. To prevent this, it is indispensable to hold the temperature of the water in the water trough c within a predetermined temperature by supplying at all times cold water to the water trough c, as shown by an arrow in FIG. 1, from a river, a fireplug, a water storage pool, etc. while draining elevated-temperature water. This means that a great quantity of water is required when using the water resistor .alpha..
By way of example, a case is considered where water at 20.degree. C. is supplied while warm water at 70.degree. C. is drained. Assuming the heat dissipation to be (70-20).times.1=50 kcal/l, i.e., that 50 kcal of heat is dissipated per 1l of water, 1,000 kW, for instance, of the output of a power source device corresponds to 1,000.times.860=860,000 kcal/h. When this value is divided by heat dissipated per 1 m.sup.3 of water (i.e., 50.times.1,000=50,000 kcal), it will be seen that 17.2 m.sup.3 per hour of water is necessary. When the water resistor is used for 8 hours, 17.2.times.8.apprxeq.140 m.sup.3 of water is necessary.
It is difficult to secure this amount of water. Besides, the water resistor .alpha. requires when using it the water trough c, a support for suspending it and a pump and piping for supplying water from the water storage pool. The overall equipment, therefore, is rather elaborate, requiring a great deal of labor for its transportation and assembly.
Further, the electric conductivity of water varies with the impurity concentration, and this means that it is difficult to obtain a stable value of resistance with the water resistor .alpha..
A further grave disadvantage of the water resistor .alpha. is that the use thereof leads to the production of a great quantity of warm drain water. When load testing of a 1,000-kW power source device is done in an urban area under the conditions noted above, draining warm water at 70.degree. C. at a rate of 17.2 m.sup.3 /h., for instance, overflow of the drained water is liable to occur depending on the draining capacity. Even if the drained water will now overflow, it will exterminate bacteria, thus reducing the drainage purifying function. In some cases, therefore, the load testing is prohibited by the drainage supervisor.
As shown above, the water resistor as a load system used for the measurement of characteristics of a power source device has the problems that generation of an electric arc is possible when it is used under a high voltage condition, that a large quantity of water is required, that elaborate equipment and labor are required, that the resistance provided is instable and that a great quantity of warm water is drained.
Further, the input power to the electrode section varies due to various causes. Although it may be held constant with suitable means by monitoring it at all time, from the standpoint of energy saving a device for automatically holding the input constant is necessary.
Further, where the main electrode section is used under a high voltage condition, the closer to the main electrode section the higher the interelectrode current density is, and the greater heat is generated. If the surface temperature of the high voltage main electrode section is quickly increased to generate air bubbles, an arc discharge is liable to result. In the event if an arc discharge is produced, it is liable to lead to a large accident. Therefore, it is necessary to provide safety measures.